1. Field of the Invention
The present invention relates in general to a method of producing a semiconductor device and more particularly to a method of forming a silicone resin film for protecting a semiconductor substrate on the substrate and then removing the film from the substrate.
2. Description of the Prior Art
Silicone resin, which contains organopolysiloxane, is superior in heat resistance and cold resistance. It is also superior in chemical resistance and thus hardly damaged by strong alkali and strong acid chemicals. Furthermore, it is superior in adhesion to various materials such as silicon, ceramics and metals (e.g., aluminum). Therefore, it is widely used in various fields.
Horinouchi et al. (1990) Technical Digest of the 9th Sensor Symposium, pp. 19-22 discloses a silicon wafer that is covered with a coating resin, except the front surface thereof (see FIG. 2).
Japanese Patent Second Publication JP-B-52-44703 discloses a method of producing a semiconductor device that has a npn transistor embedded in the surface of a substrate thereof.
In this method, at first, the substrate is irradiated with gas plasma such as an oxygen or argon plasma so as to decrease the current amplification factor of the transistor to a predetermined value. Then, the substrate is subjected to a heat treatment so as to increase the current amplification factor to the desired value.
Japanese Patent Second Publication JP-B-60-11458 discloses a method of producing a semiconductor device, in which a silicone resin is used, particularly as an insulating layer's material. In this method, at first, aluminum is deposited on a semiconductor's substrate 11. Then, the deposited aluminum is etched to form a first layer wiring 12 on the substrate 11. Then, a silicone resin layer 13 having a thickness of about 100 nm is formed so as to cover the first layer wiring 12 therewith (see FIG. 2(a)). Then, the silicone resin layer 13 is optionally heated to harden the same. Then, a patterning mask 17 such as photoresist or phosphosilicate glass (PSG) is formed on the silicone resin layer 13 (see FIG. 2(b)). Then, the exposed portion of the silicone resin layer 13 is oxidized to silicon oxide 16 by irradiating the semiconductor substrate 11 with an oxygen plasma for about 15 min under an oxygen gas pressure of 1 Torr at a power of 100 W (see FIG. 2(c)). Then, the thus formed silicon oxide 16 is removed by etching with a hydrofluoric acid containing solution (see FIG. 2(d)).
If the method according to JP-B-60-11458 is applied to remove a silicone resin film for protecting a semiconductor substrate, which film, has a much greater thickness (at least 10 .mu.m) than that (about 100 nm) of JP-B-60-11458, it is very difficult to completely oxidize the silicone resin film to silicon oxide, even if the power and the period of time of the irradiation of JP-B-60-11458 are increased to a great extent. If a silicone resin film is irradiated with the oxygen plasma under the same conditions as those described in JP-B-60-11458, a transistor embedded in the surface of a semiconductor substrate may be greatly lowered in the current amplification factor, as shown in FIG. 3 of JP-B-52-44703. Furthermore, when a silicone resin which is reinforced with filler is used for increasing the strength of a semiconductor substrate and thus for forming a diaphragm of semiconductor pressure sensor, it may be impossible to completely oxidize the silicone resin layer to silicon oxide by the method of JP-B-60-11458.